An automatic gate arrangement, such as described in German utility model No. 8,107,649, has a noncontacting proximity detector such as an electric eye that operates a side-swinging gate. A post of generally cylindrical shape has fixed upper and lower parts separated by a middle part of which the normally C-shaped gate is carried. An electric motor in the post is connected through an appropriate transmission to the middle part to pivot it about the upright post axis so as to oscillate the gate between a closed position across the path and an open position parallel to it. To prevent injury there is a slip coupling interconnecting the middle part or gate to the drive so that, if an excessive force is extended against the gate or pivoting of the gate is blocked with such a force, the gate can move independently of the drive.
Typically the gate structure itself is quite complex. It is welded together from a multiplicity of pieces and must be perfectly aligned for proper functioning. Any misalignment will in the long run damage the gate mechanism. Such welded construction is expensive and complex. In addition it makes subsequent servicing quite difficult, and leaves corrosion-prone weld spots on the outside of the post.
The final assembly of the gate mechanism must be by means of screws which invariably protrude or are recessed at the locations where they pass through the cylindrical outer wall of the post,. Thus the appearance of the column is not good, since the protruding regions can catch on clothing and the recessed regions become filled with dirt.